I want to work with everything my camera records, not a compressed, pre-processed in-camera JPEG that has thrown away up to three quarters of what was originally recorded. For me the JPEG has too much loss of definition and too much loss of flexibility. I want the flexibilty to work with the image to meet MY standards, not the standards of some engineer who wrote the inflexible in-camera JPEG processing.

In a nutshell, in-camera JPEG processing irreversibly ruins the image. You can never get back what the camera has thrown away and you cannot undo the blurring of the in-camera noise reduction.